A multiple, or accumulator bet, is a bet on a number of outcomes occurring. A multiple bet wins if, and only if, all the selected outcomes occur. Typically, the separate odds for each of the outcomes are multiplied together to give odds for all outcomes to occur together. For example, a user might bet on Newcastle, Chelsea and Liverpool all to win their respective matches. If the odds for each, expressed as digital odds, were 2.5, 1.8, 2.9, then the user might bet £10 at odds of 13.05 (2.5×1.8×2.9) that all three win. If they all win then the user wins £120.50 and if one or more fail to win the user will lose £10. The attraction for users is that they get larger odds by combining several favoured outcomes, where the odds are short.
Since it is impossible for a bookmaker to hedge the risk on an individual multiple bet, the bookmaker has to accept some level of risk. For example, a user may place a £15 bet on a combination of 8 outcomes. If all 8 occur, then the bookmaker may, for example, have to pay out £47,000, but if one does not occur the bookmaker will win £15. There is no way to place a single bet, or combination of single bets, that cover the potential payout.
The inventors have determined that where liability is looked at over a very large number of multiple bets, sufficient information can be provided to place hedging bets that can significantly reduce the risk involved.